Cooking belt

ABSTRACT

A grilling belt includes a flexible support having first and second major surfaces, an extruded fluoropolymer layer overlying the first major surface, and a cast or skived fluoropolymer layer overlying the extruded fluoropolymer layer. Another grilling belt can include a support having first and second major surfaces, and a first fluoropolymer film overlying the first major surface. The support can include a first fabric having a first bias angle, and a second fabric laminated to the first fabric and having a second bias angle different from the first bias angle by between 20° and 160°.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority under 35 U.S.C. §120 and is acontinuation of U.S. patent application Ser. No. 13/158,182, entitled,“COOKING BELT,” by Hua Fan, Anne B. Hardy, Timothy P. Pollock, andEphraim P. Lin, filed Jun. 10, 2011, which claims priority under 35U.S.C. §119(e) to U.S. Provisional Patent Application No. 61/354,104,entitled “COOKING BELT,” by Hua Fan, Anne B. Hardy, Timothy P. Pollock,and Ephraim P. Lin, filed Jun. 11, 2010. Each patent application citedherein is hereby incorporated by reference in its entirety.

FIELD OF THE DISCLOSURE

This disclosure, in general, relates to a cooking belt.

BACKGROUND

In the food industry, particularly in relation to commerciallyprepackaged and prepared foods or restaurants, businesses are turning tofaster methods of cooking food in a uniform manner. In addition, suchbusinesses are seeking to streamline operations including cleanupoperations and are seeking to reduce the risk of employee injury.

In an example, commercially prepackaged food products or commerciallyprecooked foods can be cooked on a cooking belt. In another example,meat can be cooked on a flat surface (i.e., standard stoveconfiguration) with heat only from below. Non-stick cooking surfaces canprevent sticking of the food product to the cooking surface. Reducedsticking results in reduced effort used to remove the cooked foodproduct from the surface. The reduced sticking also reduces burntresidue that is to be scraped off the cooking surface so that subsequentfood products to be cooked do not stick. However, continued use and wearof the non-stick surface can diminish the non-stick properties. As such,further improvements to non-stick cooking surfaces are desired.

SUMMARY

In an embodiment, a grilling belt can include a flexible support havingfirst and second major surfaces, an extruded fluoropolymer layeroverlying the first major surface, and a second fluoropolymer layeroverlying the extruded fluoropolymer layer. The second fluoropolymerlayer can be a cast fluoropolymer layer or skived fluoropolymer layer.

In another embodiment, a grilling belt can include a support havingfirst and second major surfaces, and a first fluoropolymer filmoverlying the first major surface. The support can include a firstfabric having a first bias angle, and a second fabric laminated to thefirst fabric and having a second bias angle different from the firstbias angle by between 20° and 160°.

In a further embodiment, a grilling system can include first and secondrollers, a heat source, and a grilling belt looped around the first andsecond rollers. The grilling belt can have first and second ends joinedtogether. Further, the grilling belt can include a flexible supporthaving first and second major surfaces, an extruded fluoropolymer layeroverlying the first major surface, and a second fluoropolymer layeroverlying the extruded fluoropolymer layer. The second fluoropolymerlayer can be a cast fluoropolymer layer or skived fluoropolymer layer.

In yet another embodiment, a method of forming a grilling belt caninclude providing a first flexible support having first and second majorsurfaces and first and second ends, laminating a first fluoropolymerlayer overlying the first major surface, and laminating a secondfluoropolymer layer overlying the extruded fluoropolymer layer. Thefirst fluoropolymer layer can include an extruded film.

In still another embodiment, a method of forming a grilling belt caninclude providing a flexible support having first and second majorsurfaces and first and second ends, extruding a first fluoropolymerfilm, casting a second fluoropolymer film overlying the firstfluoropolymer film, and laminating the first fluoropolymer film to thefirst major surface of the flexible support.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure may be better understood, and its numerousfeatures and advantages made apparent to those skilled in the art byreferencing the accompanying drawings.

FIG. 1 includes an illustration of a cross-section of an exemplary sheetmaterial.

FIG. 2 includes an illustration of an exemplary reinforcement material.

FIG. 3 includes an illustration of a cross-section of a portion of anexemplary sheet material.

FIGS. 4 and 5 include illustrations of exemplary cooking belt systems.

The use of the same reference symbols in different drawings indicatessimilar or identical items.

DETAILED DESCRIPTION

Grilling or cooking belts are often used for the production ofcommercially precooked and prepackaged food. The cooking belts can beused in a continuous process for the preparation of the food,significantly increasing productivity over a static surface, such as agrill. However, the continuous movement of the belt can result instresses to the components, leading to wear and eventually to replacingthe belt. Cooking belts extend to lengths up to hundreds of feet andreplacement of such belts can be complicated and time consuming, thuscausing significant production delays.

Generally, the belts are replaced when the ability of the cookingsurface to release the food product is reduced. The failure of thecooking surface is often the result of the formation of splits in thesurface. The splits can expose underlying components of the cookingbelt, such as a reinforcement material that may not have the samerelease properties as the overlying non-stick surface. Additionally, thesplits can trap liquids or greases, and provide a path for the liquid orgrease to reach the fibers of the reinforcement material. Once liquid orgrease has penetrated the reinforcement material, residues from theliquid or grease can abrade the reinforcement material during furtheruse, reducing the mechanical properties of the belt, leading topotential breakage of the belt.

Applicants discovered that in particular instances splits, which tend toextend along either fill or warp direction, depending on the style ofgreige good, can form on the points of overlap of the fill and warpyarns. The splits can form due to the shearing stress, such as from themovement of the belt around rollers. If allowed to propagate, suchsplits can permit grease and other liquids to infuse into fibroussupports, leading to embrittled belts with reduced strength and stressresistance.

In a particular embodiment, a sheet material includes a low surfaceenergy polymer, such as a fluoropolymer. Such a sheet material can be inthe form of a grill sheet, a cooking belt, a film, a coating, or acombination thereof. In an embodiment, a sheet material particularlysuitable as a cooking belt includes a reinforcement material and afluoropolymer film overlying the reinforcement material. In an example,the fluoropolymer film is an extruded fluoropolymer film, such as anexpanded fluoropolymer film. Optionally, a skived or cast fluoropolymerfilm can be placed to overlie the extruded fluoropolymer film. Such anembodiment can prevent split propagation, leading to improved mechanicalproperties and belt life.

In the embodiment illustrated in FIG. 1, a sheet material 100, such as acooking sheet, includes a reinforcement material 110 and a fluoropolymerlayer 104 overlying the reinforcement material 110 on one or both sidesof the reinforcement material 110. A upper layer 102 can be disposed onor can overlie the fluoropolymer layer 104, and, optionally, an bottomlayer 114 can be disposed under or can underlie the fluoropolymer layer104. As described herein, the terms “over” or “overlie” are used todescribe locations relatively closer to a cooking surface or the surfaceintended to contact an item, such as food, to be heated. The terms“under” or “underlie” describe locations relatively further from thecooking surface.

As illustrated, the upper layer 102 forms a cooking surface 108. Absentthe upper layer 102, the fluoropolymer layer 104 can form the cookingsurface 108. In addition, the bottom layer 114 forms a contact surface112 to contact a support or rollers. Absent the bottom layer 114, thefluoropolymer layer 104 can form the contact surface 112.

Optionally, an intermediate layer 116 can be disposed between thefluoropolymer layer 104 and the upper layer 102, and an intermediatelayer 118 can be disposed between the fluoropolymer layer 104 and thebottom layer 114. In a particular embodiment, the sheet material 100 canbe free of an intermediate layer 118 and bottom layer 114, and is in theform of a single sided laminate.

In an example, the sheet material 100 is a cooking belt, such as aclosed-loop cooking belt. The cooking belt can have length (longestorthogonal dimension) of at least 1 m, such as at least 3 meters, atleast 10 meters, or even at least 30 meters. In addition, the cookingbelt can have an aspect ratio, defined as the ratio of the length to thewidth (second longest orthogonal dimension) of at least 10, such as atleast 30 or even at least 100.

The reinforcement material 110 can include a fibrous reinforcement, suchas a woven or nonwoven fibrous reinforcement. For example, the fibrousreinforcement can be a woven fabric or an intermeshing of randomlyoriented fibrous strands. In one exemplary embodiment, the fabric is awoven glass fabric. In another exemplary embodiment, the fabric is aknitted fabric. In other embodiments, the reinforcement can include amesh of ceramic, plastic, or metallic material or sheets of compositematerials, among others. Alternatively, the reinforcement material 110can take the form of a substrate, typically a sheet. Embodiments can usesupports formed of high melting point thermoplastics, such asthermoplastic polyimides, polyether-ether ketones, polyaryl ketones,polyphenylene sulfide, and polyetherimides; thermosetting plastics,particularly of the high temperature capable thermosetting resins, suchas polyimides; coated or laminated textiles based on the abovethermoplastics or similar thermally stable resins and thermally stablereinforcements such as fiberglass, graphite, and polyaramid; plasticcoated metal foil; and metallized or metal foil laminated plastic films.In addition, exemplary embodiments include woven and non-woven materialsformed of fibers selected from aramid such as Kevlar® or Nomex®,fluorinated polymer, fiberglass, graphite, polyimide, polyphenylenesulfide, polyketones, polyesters, or a combination thereof. Inparticular, the fibrous reinforcement includes a fiberglassreinforcement that has been cleaned or pretreated with heat.Alternatively, the fibrous reinforcement can be a coated fiberglassreinforcement. In a particular example, each of the fibers of thefiberglass can be individually sized with a polymeric coating.

In an example, the reinforcement material 110 includes a fabric. Thefabric includes a plurality of yarns 106. In an example, the yarns 106are interwoven together to form the fabric. While the yarns 106 areillustrated in FIG. 1 to be uniformly distributed, the yarns 106 can bebunched together.

In a particular example, each filament of the yarn 106 can be pretreatedprior to incorporation into the yarn 106 or into the fabric. Forexample, each filament can be coated with a size coat. In a particularexample, the size coat includes a silane or other hydrophobic oroleophobic chemical that improves a bond with fluoropolymers, such as aperfluoropolymer.

The fabric can have a weight in a range of 0.7 osy to 15 osy, such as aweight of 1.0 osy to 12 osy, or even a weight of 1.5 osy to 10 osy. Thefabric can have yarns in a range of 20 to 80 yarns per inch, such as 30to 70 yarns per inch or even 40 to 65 yarns per inch in the warp or filldirections. Further, the fabric can have a thickness in a range between1.0 mil and 15.0 mils, such as a range of 2.0 mils to 12.0 mils, or inparticular, in a range of 3.0 mils to 10.0 mils.

In a particular embodiment, the reinforcement material can include aplurality of fabric layers. FIG. 2 provides an illustration of areinforcement material 200 including one or more fabric layers, such asfabric layer 202, fabric layer 204, and fabric layer 214. A fabric layer202 can include warp yarns 206 and fill yarns (weft yarns) 208. The warpyarns 206 can be oriented substantially parallel to the movementdirection of the belt. The movement direction can be the direction inwhich the belt travels during operation and can be substantiallyparallel to the length of the belt. The fill yarns 208 can be orientedsubstantially perpendicular to the warp yarns 206 and substantiallyperpendicular to the movement direction.

Alternatively or in addition, the reinforcement material 200 can includeone or more sheets of fabric including fill yarns that are askew fromthe perpendicular. For example, the fabric layer 204 can include warpyarn 210 and fill yarns 212. Fabric layer 204 can be biased such thatthe fill yarns 212 are not perpendicular to the warp yarns. For example,the fill yarns 212 can be oriented at an angle of about 10° to about 70°relative to the machine or warp direction as indicated by the warp yarns210, such as at an angle of about 15° to about 45°. Fabric layer 204 canbe left biased (the smallest angle formed between the warp and fillyarns) is on the left side relative to the warp direction) or rightbiased (the smallest angle is on the right side relative to the warpdirection). In an example, the fabric layer 214 can include fill yarnsthat are askew. In particular, the fabric layer 214 can include fillyarns that askew in a manner opposite that of the fabric layer 204. Forexample, the fabric layer 204 can be left side biased and the fabriclayer 214 can be right side biased or visa-versa.

In an example, more than one fabric layers having different fill yarnorientations can be coupled to form the reinforcement layer. Forexample, fabric layers 202 and 204 can be bonded together, such as bylaminating, with or without an adhesive, or an autogenous bondingprocess. In an example, each fabric layer can be coated with afluoropolymer coating. In particular, two or more layers can be bondedwith intermediate fluoropolymer layers, such as intermediate coatings offluoropolymer or a melt adhesive fluoropolymer. In another example, thelayers can be pre-sized with a fluoropolymer and heat laminatedtogether. In a further example, an adhesive, such as a silane adhesive,can be applied to bond the layers together. In an additional example,fiber layers, such as fiberglass layers, can be autogenously bonded inthe presence of charged gas.

In a particular embodiment, the reinforcement material 200 can includeadditional fabric layers. The additional fabric layers can biased in anopposite direction from fabric layer 204. For example, fabric layer 204can be left biased and an additional fabric layer can be right biased.In a particular example, the fabric layer 204 can have a bias angle,defined as the angle formed between the warp and fill yarns on the leftside of the fabric relative to the warp direction, of less than 90°,such as in a range of 10° to 70°, and the fabric layer 214 can have abias angle greater than 90°, such as in a range of 100° to 160°. Forexample, the fabric layer 204 can have a bias angle in a range of 15° to60°, such as a range of 30° to 45°, and the fabric layer 214 can have abias angle in a range of 105° to 150°, such as a range of 120° to 135°.The difference in bias angles between the two fabrics 204 and 214 can bein a range of 20° to 160°, such as a range of 40° to 140°, such as arange of 60° to 90°. In such an embodiment, the reinforcement material200 can include a fabric layer 202 or can be free of fabric layer 202.

Returning to FIG. 1, the reinforcement material 110 is incorporatedwithin the fluoropolymer layer 104. Alternatively, the fluoropolymerlayer 104 can be disposed on either side of the reinforcement material110. In particular, the fluoropolymer layer 104 can reside closer to thecooking surface 112.

In an embodiment, the fluoropolymer layer 104 includes a fluoropolymer.An exemplary fluoropolymer can be formed of a homopolymer, copolymer,terpolymer, or polymer blend formed from a monomer, such astetrafluoroethylene, hexafluoropropylene, chlorotrifluoroethylene,trifluoroethylene, vinylidene fluoride, vinyl fluoride, perfluoropropylvinyl ether, perfluoromethyl vinyl ether, or any combination thereof. Anexemplary fluoropolymer includes polytetrafluoroethylene (PTFE), afluorinated ethylene propylene copolymer (FEP), a copolymer oftetrafluoroethylene and perfluoropropyl vinyl ether (perfluoroalkoxy orPFA), a copolymer of tetrafluoroethylene and perfluoromethyl vinyl ether(MFA), a copolymer of ethylene and tetrafluoroethylene (ETFE), acopolymer of ethylene and chlorotrifluoroethylene (ECTFE),polychlorotrifluoroethylene (PCTFE), poly vinylidene fluoride (PVDF), aterpolymer including tetrafluoroethylene, hexafluoropropylene, andvinylidenefluoride (THV), or any blend or any alloy thereof. In anexample, the fluoropolymer includes polytetrafluoroethylene (PTFE),fluorinated ethylene propylene (FEP), perfluoroalkoxy (PFA),polyvinylidene fluoride (PVDF), or any combination thereof. Inparticular, the fluoropolymer can include polytetrafluoroethylene(PTFE), fluorinated ethylene propylene (FEP), perfluoroalkoxy (PFA), orany combination thereof. In a further embodiment, the fluoropolymer canbe a perfluoropolymer, such as PTFE or FEP.

In a particular example, the fluoropolymer includes a perfluoropolymer.For example, the perfluoropolymer can include polytetrafluoroethylene(PTFE), fluorinated ethylene propylene (FEP), perfluoroalkoxy (PFA), orany blend or copolymer thereof. In a particular example, thefluoropolymer layer 104 includes polytetrafluoroethylene (PTFE).

A upper layer 102 can be formed on top of or can overlie thefluoropolymer layer 104. In an example, the upper layer 102 includes afluoropolymer, such as a perfluoropolymer. For example, the upper layer102 can include PTFE. In another example, the upper layer 102 includes athermoplastic processible fluoropolymer. For example, the upper layer102 can include a perfluoroalkoxy (PFA), fluorinated ethylene propylene(FEP), or a blend or copolymer thereof.

In a further example, the upper layer 102 can include a blend ofperfluoropolymer and a second polymer. In an example, the second polymercan include a silicone. The silicone polymer can include a polysiloxane.For example, the silicone polymer can include a polyalkylsiloxane, aphenylsilicone, a fluorosilicone, or any combination thereof. In anexample, a polyalkysiloxane includes a polydimethylsiloxane, apolydipropylsiloxane, a polymethylpropylsiloxane, or any combinationthereof. In particular, the silicone polymer can be derived from anaqueous dispersion of precured silicone polymers. In an example, thesilicone polymer can be derived from an aqueous dispersion and caninclude precured silicone. In particular, the silicone polymer can bederived from an aqueous dispersion of precured silicone with terminalgroups or additives, such as cross-linkers. For example, the siliconepolymer can be selected from a silicone polymer dispersion availablefrom Wacker-Chemie GmbH, Munchen, Germany, such as the Wacker CT27Esilicone rubber dispersion, or available from Dow Corning, such asDC2-1266 silicone rubber. In particular, the silicone is formulated suchthat it can be used in contact with food or in medical applications,herein referred to as “at least food grade.” Further, the sheet materialcan be at least food grade, being formed of materials that can be usedin contact with food, such as permitted by the United States of AmericaFood and Drug Administration.

The blend can include silicone polymer in an amount in a range of 0 wt %to 80 wt % based on the total weight of the solids of the blend, such asa range of 0 wt % to 40 wt %. For example, the blend can includesilicone polymer in an amount in a range of 2 wt % to 30 wt %, such as arange of 5 wt % to 30 wt %, a range of 10 wt % to 30 wt %, or even arange of 15 wt % to 20 wt %. In addition, the blend can includefluoropolymer, such as perfluoropolymer, in an amount in a range of 60wt % to 100 wt %, such as a range of 75 wt % to 90 wt %, or even a rangeof 80 wt % to 85 wt %.

The fluoropolymer layers can be formed of extruded fluoropolymer, castfluoropolymer, or skived fluoropolymer. The extruded fluoropolymer canbe paste extruded and can be stretched, such as uniaxially stretched orbiaxially stretched. Stretched film that are stretched to a ratio of atleast 3:1, such as a ratio of at least 4:1 are referred to herein asexpanded. For example, the extruded fluoropolymer can be an expandedPTFE layer. The fluoropolymer layers can be formed directly on thereinforcement material 110 or can be formed as separate layers andlaminated to the structure.

In a particular example, a fluoropolymer layer includes an extruded filmand an upper layer includes a cast film or a skived film. The extrudedfilm can be an expanded film, such as a biaxially expanded layer. Forexample, an extruded film can be laminated to a coated reinforcementmaterial. A coating of fluoropolymer can be cast over the extrudedfluoropolymer film to form the upper layer. Alternatively, a separatecast film can be laminated over the extruded fluoropolymer layer. In aparticular example, each of the layers can be formed of aperfluoropolymer, such as PTFE.

For example, FIG. 3 shows a cross-section of a portion 300 of a sheetmaterial, such as a cooking belt, which includes an extrudedfluoropolymer film 302 and a cast or skived fluoropolymer film 304overlying the extruded fluoropolymer film 302. The portion 300 can belaminated to a coated reinforcement material, such as a fluoropolymercoated fabric. The extruded fluoropolymer film 302 can be expanded orstretched in either a uniaxially or biaxially. The extrudedfluoropolymer film 302 can exhibit a high degree of alignment of thefluoropolymer molecules 306 in a machined direction. When stretchedbiaxially, the fluoropolymer molecules 306 can be substantially alignedin two directions. The alignment of fluoropolymer molecules 306 canincrease the strength of the film in the direction of alignment.However, the extruded fluoropolymer film 302, particularly if expanded,can have a high permeability and can be weak in a non-machineddirection. Fluoropolymer molecules 308 in the cast or skivedfluoropolymer film 304 can be randomly oriented. In a particularexample, fluoropolymer film 304 can have a low permeability. Theresulting material can exhibit a reduction in split formation andpropagation, providing for extended belt life.

In a further embodiment, portion 300 can include additional layers. Forexample, the portion 300 can include extruded fluoropolymer filmsapplied to align at an angle to the alignment direction of the otherextruded fluoropolymer film 302. For example, the angle between thealignment directions of two extruded fluoropolymer films can be about15° to about 75°, such as about 30° to about 60°.

In an example, the extruded fluoropolymer film 302 can have a thicknessin a range of about 0.2 mils to about 3 mils. For example, the thicknessof the fluoropolymer film 302 can be in a range of 0.5 mils to 2 mils.

Returning to FIG. 1, the bottom layer 114 can be formed under or canunderlie the fluoropolymer layer 104. In an example, the bottom layer114 includes a fluoropolymer, such as a perfluoropolymer, such as PTFE.In a particular example, the bottom layer 114 includes a thermoplasticprocessible fluoropolymer. For example, the bottom layer 114 can includea perfluoroalkoxy (PFA), fluorinated ethylene propylene (FEP), or acombination thereof.

In an example, the bottom layer 114 and upper layer 102 form symmetriclayers on either side of the reinforcement layer 110. Alternatively, thebottom layer 114 and the upper layer 102 form asymmetric layers aboutthe reinforcement layer 110. In a further example, the sheet material100 can include one or the other, or both of the upper layer 102 and thebottom layer 114.

An intermediate layer 116 can be formed to overlie the fluoropolymerlayer 104, and an intermediate layer 118 can be formed to underlie thefluoropolymer layer 104. In an example, the intermediate layers 116 or118 can be formed of a fluoropolymer. The fluoropolymer can be differentfrom the fluoropolymer of the fluoropolymer layer 104. In an example,the fluoropolymer of the intermediate layer 116 or 118 can be a meltablefluoropolymer.

While not illustrated, additional layers can be included between thefluoropolymer layer 104 and the reinforcement, over the upper layer 102,or under the bottom layer 114. For example, the reinforcement layer 110can include yarns coated with a polymer, such as fluoropolymer. Inanother example, an additional coated layer can be disposed between thefluoropolymer layer 104 and the reinforcement or over the upper layer102.

In a further alternative, the sheet material 100 can be free of layersand coatings that underlie the reinforcement material 110, for example,being free of bottom layer 114. In such an example, the sheet material100 can be a single sided laminate, including layers only on one side ofthe reinforcement layer 110, except for sizing on the fabric. Inparticular, it has been discovered that embodiments of the single sidedlaminate exhibit desirable lamination strength with the reinforcementmaterial 110.

The sheet material 100 can exhibit desirable features. In particular,the sheet material 100 has a thickness of at least 2.5 mils, such as atleast 5 mils. For example, the sheet material 100 can have a thicknessin a range of 5 mils to 20 mils, such as a range of 7.5 mils to 16 mils.

In addition, the sheet material 100 exhibits desirable mechanicalproperties. For example, the sheet material 100 can have a desirabletensile strength in both the warp and fill directions. In addition, thesheet material 100 can have a desirable trapezoidal tear strength.Moreover, the sheet material 100 can retain desirable mechanicalproperties after distress. For example, the sheet material 100 canexhibit a desirable crease tensile strength and crease trapezoidal tearstrength. In addition, the sheet material 100 can exhibit a desirableMIT flex performance.

In a particular embodiment, tensile strength can be measured using ASTMD902. The sheet material 100 can have a tensile strength in the warp ormachine direction (generally parallel to length) of at least 30 lbs,such as at least 50 lbs. In particular, especially in the context of abelt, the sheet material can have a tensile strength in the warpdirection of at least 300 pounds per linear inch (PLI), such as at least375 PLI, or event at least 450 PLI. In a further example, the tensilestrength in the weft or fill direction (generally parallel to width) canbe at least 45 lbs, such as at least 65 lbs, or even at least 80 lbs. Inparticular, especially in the context of a belt, the belt material canhave a tensile strength in the fill direction can be at least 250 PLI,such as at least 275 PLI, or even at least 300 PLI.

The sheet material 100 can have a desirable trapezoidal tear strength asmeasured in accordance with ASTM D751, as modified by ASTM D4969. Forexample, the trapezoidal tear strength of the sheet material 100 in thewarp direction can be at least 3.5 lbs, such as at least 4.0 lbs.Particularly in the context of a belt, the belt material can have adesirable trapezoidal tear strength in the warp direction of at least 25lbs, such as at least 40 lbs, at least 60 lbs, or even at least 80 lbs.In another example, the sheet material 100 can have a trapezoidal tearstrength in the fill direction of at least 15 lbs, such as at least 25lbs, at least 40 lbs, or even at least 60 lbs.

In addition, the sheet material 100 can exhibit desirable tensilestrength and trapezoidal tear strength after distress, such as creasing.In particular, the tensile strength and trapezoidal tear strength can bemeasured after creasing one time with a 10 lb roller applied parallel toa fold. The tensile strength of the material after creasing with the 10lb roller is denoted as the crease tensile strength, and the trapezoidaltear strength after creasing is denoted the crease trapezoidal tearstrength. In particular, the sheet material 100 can have a creasetensile strength in the warp direction of at least 10 lbs, such as atleast 15 lbs, or even at least 17 lbs. Further, the sheet material 100can exhibit a crease trapezoidal tear strength of at least 0.5 lbs, suchas at least 1.0 lbs.

The durability of the sheet material 100 under distress can also becharacterized by the MIT flex performance. For example, the sheetmaterial 100 can have a MIT flex performance of at least 10,000, such asat least 15,000, at least 20,000, or even at least 25,000. The MIT flexperformance is measured with repetitions at 2 pounds on a ½ inch widespecimen in accordance with the folding endurance test of ASTMD2176-63J.

In a further example, the sheet material 100 exhibits low permeability.In particular, the sheet material 100 is not porous or layers that canbe porous, such as an extruded fluoropolymer film or a layer comprisingthe perfluoropolymer/silicone blend, include pores that are notsubstantially interconnected or are localized to that layer. Forexample, the sheet material 100 can have a permeability of not greaterthan 0.001 cu. in/min, as measured in accordance with ASTM D737, such ashaving a permeability of approximately 0 cu, in/min within thesensitivity of the measuring device. As such, the sheet material 100 canbe impermeable. In a particular example, a sheet material 100 includinga reinforcement layer and a layer comprising the fluoropolymer has apermeability of not greater than 0.001 cu. in/min.

Further, the sheet material 100 performs well when tested for cookingperformance. In particular, the sheet material 100 is resistant towicking of grease and charring of grease. In an example, wicking istested by subjecting the sheet to hot grease for greater than 16 hours,typically 1 week, at 400° F. When grease wicks into the fabric orcooking sheet, it tends to char and weaken the fabric. In addition, ittends to discolor both the fabric and the individual filaments.Embodiments of the sheet material 100 described above exhibit little orno wicking, little or no charring of grease, and little or nodiscoloration of the filaments or the fabric. Thus, embodiments of thesheet material 100 receive a pass rating for the wicking rating.

In a further embodiment, the sheet material forms a cooking belt. Asillustrated in FIG. 4, a system 400 includes a belt 402 and a heatsource 406. The belt 402 includes a flexible support, such as areinforcement material with a fluoropolymer layer overlying thereinforcement material. The outer surface of the cooking belt caninclude a cast or skived fluoropolymer film overlying an expandedfluoropolymer film. A control unit 410 can be used to influence theamount of heat that is provided by the heat source 406. In a particularexample, the belt material 100 has a thickness of not greater than 20mils, such as not greater than 14 mils, or even not greater than 8 mils.

As shown in the particular embodiment, the belt 402 forms a closed loopbelt. The closed loop belt is wrapped around rollers 404. Typically, thebelt 402 is flexible to allow routing around the rollers 404 andcontinual rotational movement around the rollers 404. The flexiblesupport can constitute a portion of the belt 402 or substantially theentirety of the belt 402. The belt 402 can include other portions, suchas a lacing or clasp mechanism 408. In an alternative embodiment, theends of the belt can be joined together without a lacing or claspmechanism, such as by melt fusing.

In addition, the belt 402 exhibits desirable mechanical properties, asdescribed above. For example, the belt 402 can have a desirable tensilestrength in both the warp and fill directions. In addition, the belt 402can have a desirable trapezoidal tear strength. Moreover, the belt 402can retain desirable mechanical properties after distress. For example,the belt 402 can exhibit a desirable crease tensile strength and creasetrapezoidal tear strength. In addition, the belt 402 can exhibit adesirable MIT flex performance.

In a further example, the sheet material can be used in a two beltsystem, such as the system 500 illustrated in FIG. 5. For example, thesheet material can used to form a belt 502 or a belt 508. The outersurfaces of at least the belt 502 and optionally, the belt 508 caninclude a cast or skived fluoropolymer film overlying an expandedfluoropolymer film. Each belt (502 or 508) can be heated by respectiveheat sources (506 or 510). In a particular example, a food product 512can be placed between the belts (502 or 508) and cooked. In general, thebelts (502 or 508) travel at the same speed to avoid shear in the foodproduct 512. Depending on the nature and positioning of the heat sources(506 or 510), the food product 512 can be cooked on both sidessimultaneously.

The sheet material can be formed by applying layers directly to thedispensed fabric or by laminating film to the fabric, or by combinationsthereof. For example, an expanded PTFE film can be laminated to a sideof the fabric. A film formed by skiving or by casting can be appliedover the expanded PTFE film and laminated to the expanded PTFE film.Alternatively, a layer can be cast or dip coated directly to theexpanded PTFE film, either after applying the expanded PTFE film to thefabric or prior to applying the expanded PTFE film to the fabric.

In particular, the method can include dispensing a reinforcementmaterial, such as a fabric and applying an expanded PTFE film over oneside of the reinforcement material. A cast PTFE film or a skived PTFEfilm can be laminated over the expanded PTFE film. Optionally, theprocess is performed on a single side of the reinforcement material.Alternatively, the process can be repeated or performed simultaneouslyfor a second side of the reinforcement material.

In another embodiment, the sheet material can be formed by a method thatincludes dispensing a fabric. In an example, the fabric is a fiberglassfabric that includes filaments that are individually size coated. Thefabric can be dip coated into a dispersion including a fluoropolymer,such as a perfluoropolymer. Excess dispersion can be metered from thefabric and the fluoropolymer dispersion can be heated to drive offsolvents and surfactants and to consolidate the fluoropolymer. Thecoating process can be performed one or more times, such as at least twotimes, at least three times, or even at least four times. Afluoropolymer film can be laminated to the coated fabric or a layer canbe extruded or cast onto one or more surfaces of the coated fabric.

In a particular example, the sheet material is formed through a processof coating a carrier web or a reinforcement material (e.g., the fabric)with a low surface energy, low coefficient of friction material, such asfluoropolymer. The carrier web or the reinforcement material are paidfrom a roll and coated on at least one side with a suspension includingfluorinated polymer particles dispersed in a liquid medium. In oneparticular embodiment, the suspension includes a fluoropolymer aqueousdispersion to which surfactant has been added. Alternatively, thesuspension can be free of surfactant.

A blade or metering rod is positioned to remove excess suspension fromthe carrier web. The suspension is then dried and sintered to form alayer on the carrier web. In a particular embodiment, the coatedsuspension is dried at a temperature in a range of about 150° F. toabout 300° F. and sintered at a temperature in a range of about 550° F.to about 720° F. Optionally, surfactants can be driven off the coatingprior to sintering by heating at a temperature in a range of about 500°F. to about 600° F. The thickness of the layer can be increased byrepeating the coating process. In one exemplary embodiment, the carrierweb can be coated with the suspension, the suspension dried, and asecond coating applied to the dried suspension before sintering.

In exemplary embodiments, the thickness of the fluorinated polymercoating is generally about 0.2-12 mils. For example, the thickness canbe about 0.2-4 mils, such as about 0.5-3 mils. The second layer can havea thickness of about 0.1 mils to about 5 mils, such as about 0.1 mils to3 mils, or even about 0.1 mils to 1 mil.

A second layer of fluoropolymer can be applied over the first layer. Forexample, the second layer can include a second fluoropolymer.Alternatively, the second layer can be applied by extruding a layer overthe first layer. In another example, a second layer can be laminated tofirst layer, such as through heat lamination.

A third layer of fluoropolymer can be applied over the second layer. Forexample, the third layer can include a third fluoropolymer. The thirdlayer can be applied by extruding or casting over the second layer. Inan example, the third layer can be extruded or cast over the secondlayer prior to laminating the second layer to the first layer. Inanother example, a third layer can be laminated to second layer, such asthrough heat lamination. For example, the third layer can be a skivedlayer that is laminated to the second layer. The third layer can belaminated to the second layer either prior to, after, or substantiallyat the same time as laminating the second layer to the first layer.

In a further embodiment, a cooking film can be formed using the abovedescribed method by replacing the reinforcement layer with a carrier oran extruded film. The coated film is formed on the carrier or theextruded film. In the case of coating on a carrier, the coated film issubsequently separated from the carrier to provide a free form coatedfilm. The free form coated film can be laminated to a reinforcementmaterial or an extruded film. In an example, the free form coated filmcan be laminated to an extruded film and the combination laminated to areinforcement material. In another example, an extruded film coated witha coated film can be laminated to the reinforcement material. In afurther example, an extruded film and a free form coated film can belaminated to a reinforcement material separately. A cooking belt can beformed using the above described method followed by coupling ends of thesheet material to form a closed loop belt in which the outer surface ofthe belt has nucleation structures. In another embodiment, the cookingsheet can be applied as a cover on a conveyor belt or a liner of acooking container. In an additional example, cooking surface withnucleation structures can be applied by spray coating the layer.

In particular, the sheet material, the cooking film, or the conveyorbelt is formed of materials and structures suitable for use in cookingapplications, and are not formed of materials that are not accepted forat least cooking applications by the United States Food of America andDrug Administration. In an example, the conveyor belt or film can beused in commercial cooking services. For example, the conveyor belt orfilm can be used in meat cooking processes, such as to cook bacon,chicken, mixed meat products, or any combination thereof. In anotherexample, a film can be placed into a vessel used to boil water. Ingeneral, the sheet material, cooking sheet, or film can be used to forma non-stick cooking surface with low splatter characteristics.

Particular embodiments of the sheet material exhibit desirable technicaladvantages. For example, the sheet material exhibits a resistance tosplit formation and propagation. In particular, the cooking belts havean extended durability and resistance to tear. Further, the coated beltscan be resistant to creasing, wicking of grease, and charring. Asdescribed below, testing has shown durability under strenuous conditionswith desirable cooking performance. As such, the cooking belts provide adurable film that maintains food quality.

EXAMPLES Testing Methods

CREASE TEST: The crease tensile strength and crease trapezoidal tearstrength can be measured after creasing a sample one time with a 10 lbroller applied parallel to a fold. The tensile strength of the materialafter creasing with the 10 lb roller is denoted as the crease tensilestrength and is measured in accordance with ASTM D902, and thetrapezoidal tear strength after creasing is denoted the creasetrapezoidal tear strength and is measured in accordance with ASTM D751,as modified by ASTM D4969.

Example 1

Comparative Sample 1 is a Silver 12 (commercially available from SaintGobain Corporation).

Comparative Sample 2 is a Silver 10 (commercially available from SaintGobain Corporation).

Comparative Sample 3 is a Ultra 3310 (commercially available from SaintGobain Corporation).

Comparative Sample 4 is a FG214 (commercially available from SaintGobain Corporation).

Sample 1 is prepared by applying a 1-pass coating of PTFE to a 1080glass fabric. Additionally, a 2-pass coating of PTFE is applied to a2116 glass fabric. The glass fabrics are laminated together and anadditional 2-pass coating of PTFE is applied. A 1.2 mil fluoropolymerfilm is laminated to one side of the glass fabrics.

Sample 2 is prepared by applying a 1-pass coating of PTFE to a 1080glass fabric. Additionally, a 2-pass coating of PTFE is applied to a7628 glass fabric having a fluoropolymer sizing applied to the yarns.The glass fabrics are laminated together and an additional 2-passcoating of PTFE is applied. A 1.2 mil fluoropolymer film is laminated toone side of the glass fabrics.

Sample 3 is prepared by applying a 1-pass coating of PTFE to a 1080glass fabric. Additionally, a 2-pass coating of PTFE is applied to a 128glass fabric. The glass fabrics are laminated together and an additional2-pass coating of PTFE is applied. A 1.2 mil fluoropolymer film islaminated to one side of the glass fabrics.

Sample 4 is prepared by applying a 2-pass coating of PTFE to a 1080glass fabric having a fluoropolymer sizing applied to the yarns.Additionally, a 4-pass coating of PTFE is applied to a 7628 glass fabrichaving a fluoropolymer sizing. The glass fabrics are laminated together.A 1.2 mil fluoropolymer film is laminated to one side of the glassfabrics.

Sample 5 is prepared by applying five passes of a PTFE coating to a 7628glass fabric having a fluoropolymer sizing applied to the yarns. ThePTFE coating is biased to one side of the glass fabric. A 1.2 milfluoropolymer film is laminated to the thinner side of the coated glassfabric.

Sample 6 is prepared as Sample 5, except 7 passes of the PTFE coatingare applied.

Sample 7 is prepared as Sample 5, except the fluoropolymer film has athickness of 0.9 mil.

Sample 8 is prepared by applying seven passes of a PTFE coating to a 128glass fabric. The PTFE coating is biased to one side of the glassfabric. A 1.2 mil fluoropolymer film is laminated to the thinner side ofthe coated glass fabric.

Sample 9 is prepared as Sample 8, except eight passes of the PTFEcoating are applied.

Samples 10 and 11 are prepared by applying seven passes of a PTFEcoating to a 128 glass fabric. The PTFE coating is biased to one side ofthe glass fabric. A 1.2 mil cast fluoropolymer film and a 0.3 milextruded fluoropolymer film are laminated the thinner side of the coatedglass fabric.

Sample 12 is prepared by applying seven passes of a PTFE coating to a141 glass fabric. The PTFE coating is biased to one side of the glassfabric. A 1.2 mil fluoropolymer film is laminated to the thinner side ofthe coated glass fabric.

Tables 1A and 1B illustrate the performance of the samples.

TABLE 1A Performance of Samples CS CS CS CS 1 2 3 4 1 2 3 4 Thickness(mils) 11.8 9.7 14.7 14.2 8.1 11.5 12.2 11.7 Weight (osy) 17.9 14.1 20.321.3 12.5 15.8 17.3 17.3 Coat Adh, lbs 6.5 — — 11.9 7.9 7.4 8.3 4.6 TrapTear, lbs W 15.0 17.6 27.4 17.4 13.2 46.1 31.7 25.7 Trap Tear, lbs F12.8 13.8 18.4 14.1 11.3 35.0 25.0 15.3 Tensile Str, lbs W 358 321 485424 315 450 481 489 Tensile Str, lbs F 247 207 329 295 259 294 338 289

TABLE 1B Performance of Samples 5 6 7 8 9 10 11 12 Thickness (mils) 9.99.9 9.4 10.9 12.0 11.7 10.8 15.3 Weight (osy) 14.6 14.9 13.8 16.4 18.017.6 15.0 21.9 Coat Adh, lbs 2.9 2.1 2.1 6.5 6.4 6.8 6.3 14.3 Trap Tear,lbs W 31.5 35.4 34.2 20.5 18.4 18.7 14.9 29.0 Trap Tear, lbs F 24.9 28.924.3 15.9 15.0 17.6 10.4 19.8 Tensile Str, lbs W 423 420 439 382 381 391303 529 Tensile Str, lbs F 277 273 312 257 257 249 184 308

Note that not all of the activities described above in the generaldescription or the examples are required, that a portion of a specificactivity may not be required, and that one or more further activitiesmay be performed in addition to those described. Still further, theorder in which activities are listed are not necessarily the order inwhich they are performed.

In the foregoing specification, the concepts have been described withreference to specific embodiments. However, one of ordinary skill in theart appreciates that various modifications and changes can be madewithout departing from the scope of the invention as set forth in theclaims below. Accordingly, the specification and figures are to beregarded in an illustrative rather than a restrictive sense, and allsuch modifications are intended to be included within the scope ofinvention.

As used herein, the terms “comprises,” “comprising,” “includes,”“including,” “has,” “having” or any other variation thereof, areintended to cover a non-exclusive inclusion. For example, a process,method, article, or apparatus that comprises a list of features is notnecessarily limited only to those features but may include otherfeatures not expressly listed or inherent to such process, method,article, or apparatus. Further, unless expressly stated to the contrary,“or” refers to an inclusive-or and not to an exclusive-or. For example,a condition A or B is satisfied by any one of the following: A is true(or present) and B is false (or not present), A is false (or notpresent) and B is true (or present), and both A and B are true (orpresent).

Also, the use of “a” or “an” are employed to describe elements andcomponents described herein. This is done merely for convenience and togive a general sense of the scope of the invention. This descriptionshould be read to include one or at least one and the singular alsoincludes the plural unless it is obvious that it is meant otherwise.

Benefits, other advantages, and solutions to problems have beendescribed above with regard to specific embodiments. However, thebenefits, advantages, solutions to problems, and any feature(s) that maycause any benefit, advantage, or solution to occur or become morepronounced are not to be construed as a critical, required, or essentialfeature of any or all the claims.

After reading the specification, skilled artisans will appreciate thatcertain features are, for clarity, described herein in the context ofseparate embodiments, may also be provided in combination in a singleembodiment. Conversely, various features that are, for brevity,described in the context of a single embodiment, may also be providedseparately or in any subcombination. Further, references to valuesstated in ranges include each and every value within that range.

What is claimed is:
 1. A method of cooking a food product, comprising:providing a grilling sheet comprising a flexible support having firstand second major surfaces; an extruded fluoropolymer layer overlying thefirst major surface; and a cast or skived fluoropolymer layer overlyingthe extruded fluoropolymer layer; providing a food product; and cookingthe food product on the grilling sheet.
 2. The method of claim 1,further comprising providing a heat source, wherein cooking the foodproduct includes disposing the food product on the grilling sheetadjacent to the heat source.
 3. The method of claim 2, wherein themethod further comprises providing a control unit that is adapted toinfluence the amount of heat provided by the heat source and using thecontrol unit to cook the food product at a predetermined temperature. 4.The method of claim 1, wherein the grilling sheet is a first grillingbelt.
 5. The method of claim 4, further comprising providing a secondgrilling belt and cooking the food product between the first and secondgrilling belts.
 6. The method of claim 5, further comprising providing afirst and second heat source, and heating the first and second grillingbelts with the first and second heat sources, respectively.
 7. Themethod of claim 6, wherein the food product has a first surface and anopposing second surface, and the method further comprises cooking thefood product on the first and second surfaces simultaneously.
 8. Themethod of claim 1, wherein the grilling sheet has a wicking rating ofpass after being subjected to hot grease for at least 16 hours.
 9. Themethod of claim 1, wherein the food product includes a prepackaged foodproduct, a precooked food product, or both.
 10. The method of claim 1,wherein the food product is a meat product.
 11. The method of claim 10,wherein the meat product includes bacon, chicken, or a mixed meatproduct.
 12. The method of claim 1, wherein the flexible supportincludes a first woven fabric having a weight in a range of about 0.7osy to about 15 osy.
 13. The method of claim 12, wherein the flexiblesupport includes a second woven fabric attached to the first wovenfabric.
 14. The method of claim 13, wherein the first fabric has a firstbias angle and the second fabric has a second bias angle, and thedifference between the first and second bias angles is between 20° and160°.
 15. The method of claim 14, wherein the flexible support includesa third fabric having a third bias angle different from the first andsecond bias angles.
 16. The method of claim 1, wherein the cast orskived fluoropolymer layer comprises fluoropolymer molecules that arerandomly oriented.
 17. A method of forming a grilling belt comprising:providing a flexible support have first and second major surfaces andfirst and second ends; extruding a first fluoropolymer film; casting asecond fluoropolymer film overlying the first fluoropolymer film; andlaminating the first fluoropolymer film to the first major surface ofthe flexible support.
 18. The method of claim 17, further comprisingjoining the first and second ends.
 19. The method of claim 17, whereincasting the second fluoropolymer film occurs prior to laminating thefirst fluoropolymer film to the flexible support.
 20. The method ofclaim 17, wherein laminating the first fluoropolymer film to theflexible support occurs prior to casting the second fluoropolymer film.